Primary liver cancer is the common malignant neoplasm in human with high mortality and its incidence is rising worldwide, especially in the United States. It occurs largely in the preexisting chronic inflammatory liver disorders, including chronic hepatitis and cirrhosis. Recent studies from our lab show that prostaglandin (PG) metabolism plays an important role in liver inflammation and carcinogenesis. In this grant we hypothesize that the level and activation status of prostaglandin signaling represents a key factor that determines the cellular response to transforming growth factor-? (TGF-?). Specifically, we postulate that enhanced cytosolic phospholipase A2? (cPLA2?) and cyclooxygenase-2 (COX-2) controlled PG signaling subverts TGF-?-mediated mitoinhibition and this mechanism is critically involved in liver carcinogenesis through selection and expansion of TGF-? resistant dysplastic and neoplastic epithelial cells that progress more rapidly toward malignant transformation and tumor development. Therefore, blocking PG signaling may restore the growth- inhibitory action of TGF-??and prevent hepatocarcinogenesis. This application proposes a series of experiments to evaluate the above hypotheses. Human liver cancer cells with altered expression of cPLA2? and COX-2 will be utilized to determine their response to TGF-?. siRNA for Smad2/3 will be introduced into human liver cancer cells stably expressing antisense cPLA2? or COX-2 and these cells will be analyzed for proliferation and apoptosis, in vitro and in SCID mice. Transgenic mice with targeted expression of cPLA2? and COX- 2 in the liver will be developed and utilized to determine TGF-?-regulated Smad activation, mitoinhibition, apoptosis, and hepatocarcinogenesis. The cPLA2? and COX-2 transgenic and knockout mice will be crossed with the TGF-?receptor type II knockout mice to determine liver regeneration and DEN-induced hepatocarcinogenesis. Finally, cultured hepatic stellate cells and experimental animal models will be utilized to evaluate our hypothesis that TGF-? and PG signaling in the fibrogenic hepatic stellate cells is critically involved in the pathogenesis of liver fibrosis and carcinogenesis. Results from the proposed studies are expected to provide important therapeutic implications for the chemoprevention and treatment of human liver cancer. PUBLIC HEALTH RELEVANCE: Primary liver cancer is a highly malignant neoplasm in human and currently there is no effective chemoprevention or systematic therapy. This application is proposed to examine our hypothesis that the level and activation status of prostaglandin signaling represents a key factor that determines the cellular response to TGF-? and that blocking prostaglandin signaling may restore the growth-inhibitory action of TGF-? and prevent hepatocarcinogenesis. A series of experiments will be performed to evaluate this central hypothesis. Results of the proposed experiments are expected to reveal an important link between TGF-? and prostaglandin signaling pathways in liver carcinogenesis and provide important therapeutic implications.